1. Field of the Invention
The present invention relates to a resin bonding method by irradiation with light (vacuum ultraviolet light); and a method for producing a resin article and a method for producing a microchip in which the resin bonding method is employed. The present invention further relates to a resin article and a microchip produced by such methods.
2. Description of the Related Art
In general, a method for bonding resins is performed by bonding by thermal fusion or bonding by coating an organic solvent or an adhesive. Bonding by thermal fusion is generally performed at the glass transition temperatures of resins or higher.
Microchips typically having a structure in which a pair of substrates are bonded together so as to face each other, at least one of the substrates including a microchannel in a surface, have been attracting attention. Microchips are also referred to as micro-fluid devices.
In microchips, by providing regions having various functions such as a reaction region where a reagent is placed in channels also referred to as microchannels, chips suitable for various applications can be provided. Microchips are typically applied to analyses such as gene analyses, clinical diagnosis, and drug screening in the fields of chemistry, biochemistry, pharmacy, medicine, and veterinary medicine; synthesis of compounds; environmental measurements; and the like. When microchips are used for such applications, for example, compared with the cases where existing analytical instruments suitable for similar applications are used, the following advantages can be provided: for example, (1) the amounts of a sample and a reagent necessary for an analysis can be reduced; (2) analysis time can be reduced; and (3) chips are disposable and hence safety and measurement accuracy can be enhanced in the field of medicine and the like.
Microchips have been mainly formed of glass substrates because glass substrates are easy to produce and allow optical detection. However, microchips formed of glass substrates are likely to be damaged by external impacts and the weight of such microchips is problematic upon transportation, disposal, and the like. Accordingly, developments of microchips formed of resin substrates that are lightweight but less likely to be damaged and inexpensive compared with glass substrates have been performed.
In microchips formed of resin substrates, a method for bonding the resin substrates together is important.
To bond resin substrates together, a general method for bonding resins such as thermal fusion can be employed. However, since bonding by thermal fusion is generally performed at the glass transition temperatures of resins or higher, there are cases where substrates deform upon bonding and the resultant microchips do not function. In addition, since the influence of deformation of substrates becomes severe when the width of channels is decreased or the pattern of channels is made complicated, it is difficult to make microchips highly functional by bonding performed by thermal fusion.
Deformation of resin substrates can be suppressed by bonding at lower temperature. As such a bonding method, Japanese Unexamined Patent Application Publication No. 2005-80569 discloses a microchip joining method in which a portion having no channels in a substrate having microchannels in a surface is coated with an organic solvent and the substrate is then placed on a substrate having a flat surface and these substrates are fused together.
Japanese Unexamined Patent Application Publication No. 2005-257283 discloses a microchip production method in which a polydimethylsiloxane (PDMS) substrate and a resin substrate (counter substrate) composed of a material other than PDMS are bonded together. In this production method, a PDMS substrate in a surface of which microchannels are formed and a counter substrate on a surface of which a silicon oxide film is formed are prepared. After the bonding surfaces of the substrates are subjected to a modification treatment, the substrates are bonded together with the silicon oxide film therebetween. A described example of such a modification treatment for bonding surfaces is an oxygen plasma treatment, specifically, an oxygen plasma treatment in which irradiation with excimer ultraviolet light in an oxygen atmosphere is performed (for example, paragraph [0017] of Japanese Unexamined Patent Application Publication No. 2005-257283).
Although the following is not directly related to microchip production methods, Japanese Unexamined Patent Application Publication Nos. 2005-171164 and 2004-43662 disclose a method in which surfaces of olefin resins are irradiated with light to activate the surfaces (in Japanese Unexamined Patent Application Publication No. 2005-171164, a photopolymerizable resin for surface modification is also used), the activated surfaces are coated with a resin composition such as a hot-melt adhesive or an ultraviolet curable resin, and the resins are bonded together with the composition therebetween.